This invention relates to a method of manufacturing a glass passivation semiconductor device including the step of depositing a glass passivation layer on the surface of a semiconductor junction by applying laser beams.
Recently, glass is used as a protective layer instead of silicon rubber in order to assure the electric stability of the surface of a semiconductor junction of a semiconductor device. This glass protective layer is prepared, for example, from borosilicate glass. Such glass protective layer prevents the seeping of water or the permeation of a harmful impurity, for example, Na ion.
To date, laser beams have been applied to deposit the above-mentioned glass passivation layer. A description is now given with reference to FIGS. 1 and 2 of a process of forming the layer. As illustrated in FIG. 1, metal electrodes 18 and a metal electrode 20 are respectively mounted on opposite sides of a silicon wafer 10 formed of, for example, a P.sup.+ layer 12, N.sup.- layer 14 and N.sup.+ layer 16. The metal electrodes 18 are applied as diode cathodes, and the metal electrode 20 as a diode anode.
The wafer 10 is later subjected to mesa etching to provide mesa grooves 22, each of which is filled with a powdery mixture 24 of various vitreous oxides. Later, laser beams are locally irradiated only on the proximity of the mesa grooves 22 having a width of 300 to 500 microns, thereby forming a glass passivation layer.
As seen from the oblique view of FIG. 2, laser beams are emitted from a CO.sub.2 gas laser. The laser beams are irradiated on a wafer 10 placed on a heating board 28 at 300.degree. to 500.degree. C. in an inert atmosphere, for example, N.sub.2 gas. Laser beams scan the lattice-shaped mesa grooves 22 formed in the wafer 10.
The annealing process based on the application of laser beams has drawbacks. If a large amount of radiation from CO.sub.2 gas laser beams is applied, the glass material is overheated to a red hot state; on the other hand, the CO.sub.2 gas laser beams permeate a silicon semiconductor substrate, preventing its temperature from rising; therefore, the glass does not wet to the semiconductor substrate, but shrinks and peels off.
To resolve the above-mentioned difficulties, it may be advised to apply a reduced amount of radiation from laser beams and slowly bake the silicon substrate. This process lets the silicon substrate absorb the heat of the glass material, causing the temperature of the silicon substrate to rise to a sufficiently high level to allow the glass material to wet to the silicon substrate, and consequently avoiding the occurrence of the aforementioned drawbacks. Nevertheless, the proposed process still suffers from the disadvantage that the CO.sub.2 gas laser has to be applied for a considerably long time.
The process of depositing a glass passivation layer by applying laser beams is already disclosed in a Japanese patent publication No. 55-36,184 and a Japanese laid-open patent application No. 51-151,071. The Japanese laid-open patent application sets forth a process of applying a single kind of laser beams. The Japanese patent publication No. 55-36,184 indicates a process of applying two kinds of laser beams. In the latter process, one kind of laser beams is used to bake a glass material and the other kind of laser beams is applied in scribing the semiconductor substrate.